Within the food industry, it is common practice to pack liquid and partly liquid food products in packaging containers manufactured from a packaging laminate comprising a core layer of paper or paperboard and one or more barrier layers of, for example, polymer material or aluminium foil.
An increasingly common packaging type is the “carton bottle” manufactured in a filling machine in that packaging blanks of the above-described packaging laminate are formed and sealed as a sleeve. Said sleeve is closed in one end in that a top of thermoplastic material is injection moulded directly on the sleeve end portion. The sheets of packaging laminate may be cut from a magazine reel of packaging laminate.
When the top is finished the packaging container is ready to be filled with product through the still open bottom, and then sealed and finally folded. Before the filling operation the packaging container undergoes treatment. If distribution and storage is to be made in chilled temperature the packaging container is disinfected, whereas if distribution and storage is to be made in ambient temperature, the packaging container needs to be sterilized. A conventional way of sterilizing a ready-to-fill packaging container is to use hydrogen peroxide, preferably in gas phase.
Another way to sterilize such packaging containers is to irradiate it by means of a low voltage electron beam emitted from an electron beam emitter. An example of linear irradiation by electron beam of ready-to-fill packaging containers is disclosed in the international patent publication WO 2005/002973. The electron beam emitter is cylindrical with an electron exit window positioned at one of the distal ends. The packaging container is lifted to surround the electron beam emitter during the sterilization cycle. Other examples of irradiation of packaging containers, in these cases PET bottles, are described in for example WO 2011/011079 and EP 2 371 397, the latter describing a rotary system. In these systems emitters are used having a diameter small enough to be passed through a neck portion of the bottles.
In order to monitor correct operation of the electron beam emitters, and thereby being able to secure sterility assurance level, it is common practise to perform dosimetry tests. These tests are made regularly, generally daily, throughout the lifetime of the electron beam emitter. In general, dosimetry tests involve adding a dosimeter means, i.e. a patch reacting on radiation exposure, to a packaging container to measure if a correct absorbed dose is obtained during radiation. At the same time measurements of voltage and current are made in the electron beam emitter. The current over the filament is measured. By comparing the current fed to the filament and current leaving the filament it is possible to determine the amount of electrons emitted from the filament. In addition, the voltage, i.e. the electric potential, between the electron exit window and the filament is measured. The measured value of voltage and current is then used as a set value during production of packaging containers. The current and voltage are continuously monitored during production, and as long as the value is not lower than the set value it is assumed that the packaging containers receive the correct dose.
However, the use of disposable dosimeter patches or dosimeter films requires a lot of manual work for performing the dosimeter measurements. The dosimeter films also have to be processed in a laboratory for obtaining the dosimeter values. The dosimeter films further cannot stand for high temperatures, limiting the measurement duration. There is thus a need for an automated dosimeter measurement. WO2007050007 and WO2014086674 suggest solutions using a dose measuring device having a conductor that is permanently or temporarily placed in front of the electron beam emitter window. The conductor is charged by the electron beam and a current that is proportional to the electron beam intensity may be measured and the dose may thus be calculated. These dose measuring devices will however produce a very coarse measurement of the electron beam profile since each conductor will correspond to a summarized line measurement along the extension of the conductor that is exposed to the electron beam. When placed permanently in front the window, they will present a barrier shadowing some part of the electron beam profile. Each conductor will also be heated by the electrons hitting it, presenting a risk of damaging the exit window of the electron beam emitter.
There is thus a need for an improved sensor device for dosimeter measurement for an electron beam emitter that has a resolution that is as good as or better than the resolution of a dosimeter film.